Use local button styles during forwarded X11 session over SSH

This has apparently been discussed on SuperUser as well; Suppressingfire's answer looks to me like the correct one:

Install your favorite Ubuntu GTK theme on the remote host as well;
Create a ~/.gtkrc-2.0 on the remote host, and include the theme's own gtkrc from it; e.g., if you're running Ubuntu with the ClearLooks theme on the remote host, you can add use this line:
```
include "/usr/share/themes/ClearlooksClassic/gtk-2.0/gtkrc";
```

Update from comments

The GUI way:

sudo apt install lxappearance gnome-themes-extras
lxappearance

With this method you also can change other properties like icons

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